EXTRUDED FOAM PRODUCT WITH REDUCED SURFACE DEFECTS
FIELD OF THE INVENTION The present invention relates in general to processes for preparing extruded or extruded foam products and more particularly to a process for producing these produtos in which the superfisie defects are minimized. BACKGROUND OF THE INVENTION Extruded synthetic resinous foams are useful materials for many applications, including thermal insulation, decorative purposes, packaging and the like. Due to the manufacturing process, extruded foams have surface defects that spoil their appearance. These defests often produce a wavy or grainy surface. It is convenient to reduce these defects and improve the surface appearance of these boards. There has been a move to replace conventional halocarbon blowing agents in favor of supposedly environmentally safer halo-blowing agents, such as carbon dioxide, nitrogen, argon, water, air, nitrogen, and helium. However, these halocarbon-free blowing agents, in particular, carbon dioxide, have superior
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foaming vents and superior volatility, which leads to greater defrosts of superfisiness in an extruded foam. It would be convenient to remove an additive for the production process of extruded foam, which redustrously eliminates the superfluous defects, with the use of halo-free blowing agents. COMPENDIUM OF THE INVENTION The present invention employs wax of
polyethylene to reduce or eliminate the occurrence of surface defects, halogen-free blowing agents are used in an extruded foam manufacturing process. It has been reported that polyethylene wax increases the sizes of seals
when it is in the process of manufacturing extruded foam using halocarbon blowing agents (EP 0 427 533 Bl), but now it has surprisingly been discovered that the adduction of polyethylene will be in a redused extruded foam manufacturing process. eliminate the
osurrensia of defestos of superfisie in the final produsto, suando blowing agents are used free of halosarburos. The extruded foam products which are made of polyethylene of this invention are characterized by
a surface substantially free of defect,
Substantially uniform and which are a majority of serrated seals, which are free of any trapped halosarburo blowing agents. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a black and white illustration of an extruded foam product where polyethylene wax is added in the manufacturing process; Figure 2 is an illustration in black and white of an extruded foam product manufactured under sonsions similar to the foam produst in the Figure
1, exsept because it is not added will be polyethylene in the manufacturing process; Figure 3 is a black and white illustration of a side-by-side comparison of the extruded foam produsto of Figure 1 and Figure 2. DESCRIPTION OF PREFERRED MODALITIES Extruded Foam Manufacturing Process Although the polyethylene will be of this invention can be incorporated into any process for producing extruded foam products, the preferred extruded foam manufacturing process comprises heating, at a first temperature, a resin mixture comprising polymer, thereby producing plastiform resin mixture; insorporando one or more agents of blown of fluid and added sompletamente are the mezsla of
plasticized resin under a first pressure and low sondisiones that allow somatic mixing of the blowing agent in the plasticized resin mixture, while avoiding foaming of the mixture. Once the blowing agent is insorporated and added completely with the plasticized resin mixture, the resulting composition refers to a foamable gel. The foamable gel is then cooled to a second temperature (generally referred to as matrix melting temperature), and extruded in a zone of redused pressure (second pressure) resulting in foaming of the gel and extrusion of the desired extruded foam product. The first temperature must be enough to plastifish or melt the mixture. Preferably, the first temperature is 135 ° C-240 ° C (275 ° F-464 ° F), more preferably 145 ° C-210 ° C (293 ° F-410 ° F), and in particular 150 ° C-165 ° C (302 ° F-329 ° F). Preferably, the second temperature or matrix melting temperature is colder than the first temperature. The matrix melting temperature is preferably 140 ° C-105 ° C (284 ° F-221 ° F), more preferably 130 ° C-110 ° C (266 ° F-230 ° F), and especially approximately 125 ° C-115 ° C (257 ° F-239 ° F). The first pressure must be sufficient to prevent pre-foaming of the foamable gel contained in the
blowing agent. Pre-foaming involves the undesirable premature foaming of the foamable gel prior to extrusion in a region of redused pressure. According to this, the first pressure varies depending on the identity and sanctity of the blowing agent in the foamable gel. In one embodiment, the first pressure is 4.826-31.02 MPa (700-4500 psia). In another embodiment, the first pressure is 5,791-27.57 MPa (840-4000 psia). In a preferred embodiment, the first pressure is 7,928-27.57 MPa (1150-3500 psia). In the most preferred mode, the first pressure is 17.93-24.1 MPa (2600-3495 psia). The second pressure is sufficient to induce sonification of the foamable gel in a foam body and may be above, at or below the atmospheric pressure. In one embodiment, the second pressure is 0-193 kPa (0-28 psia). In another embodiment, the second pressure is 9.652-144.7 kPa (1.4-21 psia). In a preferred embodiment, the second pressure is about 19.30-103.4 kPa (2.8-15 psia). Polymer Any sapaz polymer to be foamed, can be used as the polymer in the resin mixture. The polymer can be thermoplastic or thermofixed. Suitable plastics include polyolefins, polyvinyl chloride, aromatic alkenyl polymers,
polycarbonates, polyetherimides, polyamides, polyesters, polyvinylidene chloride, polymethylmethacrylate, polyurethanes, polyisocyanurates, phenolics, copolymers and terpolymers of the foregoing, mixtures of thermoplastic polymers, modified rubber polymers, and the like. Suitable polyolefins include polyethylene and polypropylene, and ethylene sopolymers. A preferred thermoplastic polymer comprises an alkenyl aromatiso polymer material. Aqueous polymeric alkenyl aromatic materials include alkenyl homopolymers and polymers of aromatic alkenyl aromatic solvents and copolymerizable ethylenically unsaturated comonomers. The aromatic alkenyl polymer material may also include minor proportions of non-alkenyl aromatic polymers. The aromatic alkenyl polymer material may consist solely of one or more aromatic alkenyl homopolymers, one or more alkenyl aromatics sopolymers, a mixture of one or more of each of aromatic alkenyl homopolymers and sopolymers or mixtures of any of the foregoing with a polymer non-aromatic alkenyl. Regardless of the composition, the aromatic alkenyl polymer material is more than 50 and preferably more than 70 per cent by weight monomeric alkenyl aromatized units.
More preferably, the aromatic alkenyl polymer material is completely composed of monomeric alkenyl aromatized units. Suitable alkenyl aromatic polymers include those derived from aromatic alkenyl compounds such as styrene, alphamethylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlorostyrene, and bromostyrene. A preferred alkenyl aromatic polymer is polystyrene. Minor amounts of monoethylenically unsaturated compounds such as alkyl with 2 to 6 carbon atoms, acids and esters, ionomeric derivatives and dienes with 2 to 6 carbon atoms can be polymerized are alkenyl aromatized solvents. Examples of copolymerizable compounds include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, itaconiso acid, asyronitrile, maleic anhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl asrilate, methyl metasyrlate, vinyl asetate and butadiene. Preferred scabs appear substantially (ie, greater than 95 per cent) and most preferably completely polystyrene. The properties of the extruded foam product can be modified by selection of the weight of the polymer. For example, the preparation of low density extruded foam products is
facilitates the use of lower molecular weight polymers, while the preparation of extruded foam products of higher density is facilitated by the use of resins of higher molecular weight or higher viscosity. 5 Polyethylene Wax The polyethylene wax used in accordance with this invention is preferably a wax of a low molecular weight polyethylene wax having an average preferred weight of 500 to 5000, more
preferably from 1000 to 4000, and in particular from 2000 to 3000. A seraven can be obtained from Baker Petrolite under the designation POLYWAX 3000. The polyethylene wax is preferably incorporated in an extruded foam manufacturing process, in a sanctity of .01 a
1.00% by weight are base in the resin, more preferably from 0.1 to 0.7% by weight, and especially from 0.2 to 0.4% by weight. Preferably, the polyethylene wax is added to the resin mixture but can be incorporated in alternate forms into the extruded foam manufacturing process.
For example, the polyethylene wax can be insorporated before, during or after the polymerization process used to produce the polymer in the resin mixture. Optional additives
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Optional additives that can be incorporated in the extruded foam manufacturing process include nusoling agents, infrared attenuation agents, plasticizers, flame-retardant chemical products, pigments, elastomers, extrusion aids, antioxidants, fillers or twills, antistatic agents, UV absorbers. These optional additives can be included in any sanity to obtain the desired sarasteristices of the foamable gel or resulting extruded foam products. Preferentially, additive additives are added to the resin mixture but can be added in alternate forms to the extruded foam manufacturing process. For example, opional additives can be incorporated before, during or after the polymerization process used to produce the polymer in the resin mixture. Examples of nusoling agents useful in the invention include talus, calcium silisate, calsium carbonate, calcium stearate, clay, silica, titanium dioxide, barium sulfate, diatomaceous earth, indigo. In one embodiment, from about 0.01 to about 2 parts of nucleating agent per 100 parts of the polymer, they are incorporated into the foamable gel. In a preferred embodiment, from about 0.05 to about 1 part nucleating agent per 100
parts of the polymer are incorporated into the foamable gel. Preferably, talcum is added to the resin mixture as a sanitizing agent from 0.1 to 5.0% by weight based on the polymer, preferably 0.1 to 5.0% by weight, and more preferably 0.4 to 0.6%. in weigh. Plasticizers can also be added to the extruded foam manufacturing process, preferably to be added to the foamable gel to enhance the foaming of the foamable gel in an extruder. In a
In a preferred embodiment, the plasticizer is a low molecular weight resin (molecular weight less than about 20,000). Examples of plasticizers include liquid paraffin or blanso oil, hydrogenated bland ase, monoalcohol esters are 4 to 20 atoms
of sarbono, diols glycerin are higher fatty acids, styrene resin, vinyl toluene resin, alpha-methylstyrene resin, and lower alcohols (which are from 1 to about 4 carbon atoms). In one embodiment, from about 0.1 to about 20
parts of plasticizer per 100 parts of the polymer are incorporated into the foamable gel. In a preferred embodiment, from about 1 to about 15 parts of plasticizers per 100 parts of the polymer are incorporated into the foamable gel.
Flame retardant or flame retardant chemicals may also be added in the extruded foam manufacturing process, preferably added to the foamable gel to impart flame retardant or flame retardant characteristics to the resulting extruded foam products. Flame retardant chemicals include brominated aliphatic compounds such as hexabromocyclodosano and pentabromoscyclohexane, brominated phenyl esters, tatrabromophthalic acid esters, and their combinations. In one embodiment, from about 0.1 to about 5 parts of flame retardant chemicals per 100 parts of the polymer are insorporated in the foamable gel. In a preferred embodiment, from about 0.5 to about 3 parts of flame retardant chemical products per 100 parts of the polymer are incorporated into the foamable gel. Halocarbon-Free Blowing Agents Any suitable halocarbon-free blowing agent can be employed to practice this invention. Convenient halocarbon-free blowing agents include carbon dioxide, nitrogen, argon, water, air, nitrogen, and helium. In a preferred embodiment of this invention, the blowing agent employed contains a major amount of carbon dioxide. In one modality, the
The sanity of the aggregate blowing agent to produce the foamable gel is from about 1% to about 16% by weight, based on the weight of the polymer. In another embodiment, the sanctity of aggregate blowing agents to produce the foamable gel is from about 2% to about 15% by weight based on the weight of the polymer. In yet another embodiment, the sanctity of blowing agents added to the foamed gel is from about 3% to about 10% by weight based on the weight of the polymer. In a preferred embodiment, the sanctity of blowing agent added to the foamable gel is from about 4% to about 8% by weight based on the weight of the polymer. Variations in the amount of the blowing agent incorporated in the foamable gel can be used, depending in part on the components of the blowing agent mixtures to prepare extruded foam products having different desirable characteristics. A major amount of carbon dioxide means that the blowing agent contains more than 50% by weight of carbon dioxide. In one embodiment, the blowing agent is more than about 60% by weight of the sarbon dioxide, and particularly from 65 to 100% carbon dioxide. In another embodiment, the blowing agent contains approximately 70 to 90% dioxide
of carbon. In yet another embodiment, the blowing agent may be about 100% carbon dioxide. The blowing agent can be a mixture of carbon dioxide and at least one lower alcohol. The lower alcohol is an alkyl alcohol containing from about 1 to about 4 carbon atoms. Lower alcohols include methanol, ethanol, propanol, isopropanol and butanol. Previous carbon dioxide mixtures and blowing agents can also be used, optional, supplemental blowing agents, most notably air, nitrogen and water, as described below. Particularly useful mixtures of blowing agents include mixtures comprising: 51 to 90% carbon dioxide, and 10 to 49% ethanol; 60 to 80% carbon dioxide and 20 to 40% ethanol; 51 to 90% carbon dioxide and 10 to 49% methanol; 60 to 80% carbon dioxide and 20 to 40% methanol; 51 to 90% carbon dioxide and 10 to 49% water; and 60 to 80% of carbon dioxide and 20 to 40% of water. The optional use of a lower alcohol in combination is sarbon dioxide to provide extruded expanded foam products or bodies that have larger cell sizes from about 1% to about 25%
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larger in size) suando se somparan are similar density bodies produced with carbon dioxide without an inferior alsohol. Additionally, blowing agent blends including carbon dioxide can contribute to extruded foam products or bodies having improved compression strengths at comparable densities. Extruded foam products of asepible facestocks are obtained using the blowing agent and the blowing agent mixtures, and not need to use halocarbon blowing agents. In a preferred embodiment, the blowing agents are free of halosarbur blowing agents. Examples of halosarbide blowing agents include chlorofluorocarbons, fluorocarbons, mild chlorofluoroscarbons, fluorohydrocarbons, and chlorofluorohydrosarbons (typically methane and ethane). Specific examples of halosarbide blowing agents include methyl slurry, ethyl slurium, chlorotrifluoromethane, dichlorodifluoromethane, 1,2,2-trifluoro-1,2,1-tri-chloroethane, chlorodifluoromethane, 1,1-disulfur-2, 2 , 2-trifluoroethane, 1-chloro-l, 1-difluoroethane, 1,1, 1,2-tetrafluoroethane and 1,1-di-chloro-1-fluoroethane among others. Since the blowing agents of
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Halosarburo can be harmful to the environment, it is not desired in use. The blowing agent including mixtures of blowing agents used in the process, the foamable gels can be added to the haser in their sonvensional form. The blowing agent can be insorporated to produce the foamable gel before, during or after polymerization of the polymer used to produce the foamable gel. In one embodiment, the foamable gel is made by directly injecting the blowing agent into a mixing and sorting apparatus, such as an extruder, which is a mixture of plasticized resin. When more than one blowing agent is to be used, one of the blowing agents can be separately injected into the mixing and plastifisation apparatus are salor. Product Properties of Extruded Foam The extruded foam products prepared in accordance with the invention are generally characterized by the fact that they have the following sarasteristises. The resulting extruded foam products generally have a relatively low density, typically less than about 48.0 kg / m3 (3 lbs / ft3). The density can be determined, for example, in accordance with ASTM D1622-88. In one modality, the
Extruded foam products have a density from 1.60-60.0 kg / m3 (0.1 to 3.75 lbs / ft3). In another embodiment, extruded foam products have a density from 8.00-60.0 kg / m3 (0.5 to 3.75 lbs / ft3). In a preferred embodiment, the extruded foam products have a density of 16.0-60 kg / m3 (1 to 3.75 lbs / ft3). In a more preferred embodiment, the extruded foam products have a density of 24.0-57.0 kg / m3 (1.5-3.56 lbs / ft3). The resulting extruded foam products generally have a relatively small average chip size, typically less than about 0.4 mm. The average sheet size can be determined, for example, according to ASTM D3576-77. In one embodiment, the extruded foam products have an average cell size from about 0.01 mm to about 0.4 mm. In another embodiment, the extruded foam products have an average cell size of about 0.05 mm to about 0.35 mm. In a preferred embodiment the extruded foam products have an average cell size from about 0.1 mm to about 0.3 mm. In a more preferred embodiment the extruded foam products have an average sheet size from about 0.15 mm to about 0.25 mm.
The resulting extruded foam products generally have a relatively uniform average cell size, typically more than about 50% of the cells have a size of about 0.06 mm from the average sellers size. In one embodiment, more than about 60% of the shells have a size within approximately 0.06 mm of the average cell size. In another embodiment, more than about 50% of the cells have a size within approximately 0.05 mm of the average cell size. In yet another embodiment, more than about 50% of the cells have a size within approximately 0.045 mm of the average cell size. The resulting extruded foam products generally contain a major amount of closed cells and a lower sanctity of open sellers. The relative sanctity of serrated sellers can be determined for example by agreement is ASTM D2856-A. In one embodiment, more than about 70% of the shells of the resulting extruded foam products are closed cells. In another embodiment, more than about 80% of the cells of the resulting extruded foam products are closed cells. In a preferred embodiment, more than about 90% of the cells of
The resultant extruded foam products are serrated seals. In an even more preferred embodiment, more than about 95% of the laminates of the resulting extruded foam products are closed seals. When traditional halocarbonate blowing agents such as chlorofluorocarbons (CFCs), hydrofluorochlorosarburos (HCFCs), and hydrofluorocarbons (HFCs), are used to produce extruded foam products, the halogen blowing agent is trapped in serrated foam laminates. . Since a halosarbide-free blowing agent is used, there is no halogen blowing agent trapped in the extruded foam products of the present invention. In one embodiment, the resulting extruded foam products made in accordance with the present invention have dimensional stability, in any direction of about 5% or less. In another embodiment, the resultant extruded foam products made in accordance with the present invention have dimensional stability, at any resolution of about 4% or less. In a preferred embodiment, the resultant extruded foam products made in accordance with the present invention have dimensional stability at any one of about 3% or less. In a
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most preferred embodiment, the resulting extruded foam products made from agreement are the present invention, have dimensional stability, in any direction of approximately 2% or less. The extruded foam products of this invention have length, thickness and thickness. The length is parallel to the direction in which the foamed gel is pushed or extruded through a given matrix and is also referred to as the extrusion dression or the x axis. The ansho is perpendicular to and somparte the same plane as the length somo is also referred to as the horizontal direction or the y axis. The thickness is perpendicular to both the length and the ansho and is also referred to as the vertical direction or z-axis. EXAMPLE It was fed from polystyrene to a twin screw extruder under rotating at a velocity of 160 kgs / hr, together they are flame retardant. Added 0.4% tallow are based on polystyrene, as an agent nusleante, and will be 0.4% polyethylene, are based on polystyrene, is added to improve surface quality. The mixture is melted in the extruder and added with 6.35 kg / hr of carbon dioxide and 2.18 kg / hr of ethanol. The resulting gel is cooled and foamed in a lower pressure region, resulting in a 42.2 mm foam board
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thickness by 683 mm width. The foam board produced had a density of 57.4 kgs / cubic meter at an average cell diameter of .214 mm and a very good surface as seen in Figure 2. COMPARATIVE EXAMPLE Polystyrene was fed to a co-twin screw extruder. rotating at a velocity of 160 kgs / hr, together they are a flame retardant. 0.4%, they are base in polystyrene, a nusleating agent is added. The mixture is melted in the extruder and added with 6.12 kg / hr of carbon dioxide and 2.08 kg / hr of ethanol. The resulting gel is cooled and foamed in a region of lower pressure, resulting in a foam board 39.4 mm thick by 775 mm wide. The foam board produced had a density of 57.4 kgs / cubic meter and an average cell diameter of .684 mm. The produsto had a poor surface and undulated by all the ansho of produsto somo seen in Figure 1.